The invention relates to an improved pneumatic brake-clutch, of the kind used in driving machines with start-stop movement, such as presses, cutters and so forth, in which the brake-clutch works as a safety element, for braking in the same takes place in the absence of air pressure and hence any failure in the supply of compressed air shall cause previously compressed springs to disconnect and brake the machine.
The improvements of the invention applicable to the aforesaid type of pneumatic brakes-clutches primarily focus on a new arrangement in mounting the discs that rub against the linings in order to improve the braking torque that is known to be a result of the pneumatic pressure supplied, the piston surface and the friction coefficient of the linings. Thus, since the friction linings available in the market are very specific and the network pneumatic pressure is also specific, the invention allows the piston surface or, in other words, the diameter of the cylinder in which it works to be increased, to yield brakes-clutches with a braking strength or torque greater than others of similar dimensions in the market.
The brakes-clutches that are used in machines such as presses, shears and the like generally comprise a central cylindrical and substantially flat body that is mounted upon the relevant axis that is to be driven-stopped, mounting taking place with the assistance of cotter pins, locking rings and so forth.
The central body in turn comprises two side covers that are positively fixed to each other through the central hub used for coupling to the shaft, and a vertical intermediate plate that turns with the covers, but having axial movement, propelled on one side by springs that rest on one of the covers and drive the same towards the facing cover, whereas in the opposite direction a piston positively fixed to the same central plate acts to provide such axial movement, all so that combined with a cylinder positively fixed to the adjacent cover the same is strongly displaced when compressed air enters into the cylindrical cavity, the resulting effort being powerful enough to overcome the spring force thereby to press the central plate against the facing cover.
Close to one of such covers, inside the central body as such and projecting from the periphery thereof, there is a ring carrying friction linings, which ring is fixed to the machine casing, the area with linings lying between the brake cover and the central plate, so that in the absence of air pressure the ring shall be locked between the two, holding the brake-clutch and the shaft it controls still.
Similarly, another ring carrying friction linings is positively fixed to the machine driving wheel, lying between the central plate and the cover on the side of the clutch, so that when the cylinder cavity is filled with compressed air, the pressure shall move the central plate, overcoming the spring force and causing the brake to be freed, pressing at the same time the lining on the ring positively fixed to the wheel, causing by friction the clutch-brake and the shaft positively fixed to the same to be started, at the same speed as the driving wheel.
Now then, these brake-clutches, having a diameter that is larger than their length, and driven by a single ring with linings on the brake side, and a ring on the clutch side, have a number of disadvantages and problems for, bearing in mind that the coefficient of friction of the linings is of a magnitude that is standard in the market and that the air pressure available in garages generally is also standard, if the diameter of the clutch-brake is the same, the only possibility there is of improving the torque is increasing the cylinder section. Heretofore, for a given diameter of the central body, the brake-clutch was provided with rings with linings the diameters of which at the friction area were: the largest, equal to the outer diameter of the central body; and the smallest, as large as possible bearing in mind that the circular ring lying between the two must have a surface such that the specific pressure on the linings lie within the pressures recommended by their manufacturer.
Furthermore, the outer diameter of the cylinder and the respective piston are at most equal to the smallest diameter of the lined ring, and it is hence possible for the friction surface of the cover on the brake side to reach out to the linings as such.
It must also be borne in mind that these brake-clutches are fixed to the shaft usually by means of cotter pins and the arrival of driving air takes place through the center of the shaft, communicating with transverse holes that meet matching holes on the brake-clutch. Now then, the cotter pins need a very accurate adjustment, and yet they are prone to become loose because of the start-stop operation of the assembly. In addition, as the air ducts have to be impervious, outer discs have to be provided that carry sealing gaskets, thus complicating mounting.